In radio frequency applications, waveguides are often used for guiding electromagnetic energy from one place to another. Waveguides are also sometimes used as radiating or receiving elements, for example as a horn antenna.
Often, there is a desire to include an electromagnetic wave absorbing load within a waveguide. For example, a load may be used as a termination. A termination can absorb reflected power from a component (e.g., an antenna, circulator, isolator, or the like) to help prevent the reflected power from disrupting system operation.
Generally speaking, a load comprises a lossy material disposed within the waveguide. The lossy material converts incident electromagnetic energy into heat. Lossy materials can include materials with dielectric (E-field) loss, magnetic (H-field) loss, or both.
Because the incident electromagnetic energy is converted into heat, power dissipation within the load can present problems. Typically, the loss material is a relatively poor conductor of heat, thus high power levels or long irradiation times can cause the load to heat to unacceptable temperatures. Accordingly, some loads use complex water cooling arrangements to manage power dissipation and increase power levels which can be accommodated. Water cooling adds cost, complexity, and weight, and is undesirable in some applications.
Generally, it is desirable for a load placed into a waveguide to provide a good impedance match to the waveguide to minimize energy reflected back from the load and provide good power transfer into the load. Reflected energy can, for example, cause damage to electronic components or result in degradation in the performance of the radio frequency system.
Conventionally, to provide a good impedance match has been achieved by using smoothly tapered geometries for the load. For example, known loads are in the form of a pyramid or inverted pyramid shape. The pyramid is positioned within the waveguide, with the point end of the pyramid facing toward the source of electromagnetic energy. Unfortunately, typical loads are relatively large, extending several wavelengths along the waveguide.